The present invention relates to an ultrasonic motor and an electronic apparatus equipped with such an ultrasonic motor for friction-driving a moving member by ultrasonic vibrations caused by utilizing compression/expansion movement of a piezoelectric vibrator.
A conventional ultrasonic motor capable of realizing a stepping drive by a predetermined moving amount without using such a position detecting means as an encoder is constructed as described in Japanese Patent Publication No. JP-B-3-207281 (1991), or No. JP-B-4-38180 (1992).
FIG. 27 is a top view of the conventional ultrasonic motor capable of realizing a stepping drive by a predetermined moving amount without employment of such a position detecting means amounts as an encoder. A moving member 2701 has 4 convex portions 2701a and is in contact with a vibrating member 2702 having a projection portion 2702a.
FIG. 28 represents a positional relationship between a moving member 2801 and an electrode pattern structure of a piezoelectric vibrator 2803 fixed to a vibrating member 2802.
FIG. 29 is an operational explanatory diagram for showing vibration conditions when the conventional ultrasonic motor is driven in a stepping mode. Symbols shown in FIG. 29 correspond to those of FIG. 28. At a standing wave 1, A, B, C are combined with inverted A, inverted B, inverted C, respectively, which are vibrated under mutual phase shifts of 180.degree.. As a result, a force is given to the convex portion 2801a of the moving member along a direction from the loop of the standing wave to the node thereof, and then this convex portion 2801a is positioned above the node of the standing wave 1 where the force becomes balanced. For another standing wave 2, B, C, inverted A are combined with inverted B, inverted C, A, respectively. For a further standing wave 3, C, inverted A, inverted B are combined with inverted C, A, B, respectively. The position of the node is stepwise moved by successively repeating the standing wave 1, the standing wave 2, the standing wave 3, the standing wave 1 in this order. Thus, the convex portion 2801a of the moving member 2801 is moved by a moving amount equal to this stepwise movement. In other words, with respect to the electrode pattern structure of the ultrasonic motor shown in FIG. 28, it is so constructed that the moving member 2801 is rotated by 1 turn with 12 steps.
However, in such a conventional ultrasonic motor capable of performing the stepping drive by a predetermined moving amount without using the position detecting means, e.g., the encoder, since the moving amount of the moving member in a stepping drive mode is determined by such a moving amount as the interval of the standing waves, or the node of the standing wave, the stepping angle of the moving member cannot be made smaller than the interval between the nodes of the standing waves, or the moving amount of node of the standing wave.